Energy harvesting wireless — the secret to M2M's success

A few years ago, M2M communication was an expensive niche application that required complex networking. But with technological developments and the flexible capabilities of cloud services, both the infrastructure and the products have made it possible to provide a great deal of information for M2M applications cost-effectively, using wireless modules.

The deeper the interconnection of these devices, the more flexibility is demanded of the technologies. That’s a major reason why energy harvesting wireless technology is increasingly being adopted within M2M devices, products and building automation systems.

Today, M2M is considered a future-oriented growth market with high expectations. The predictions range from over 300 million by 2017 to 50 billion devices connected to the Internet by 2020. Deploying the millions of distributed devices lead to a challenge: How should they be powered and how will they communicate? One solution is energy harvesting wireless technology.

Wireless sensors and relay receivers enable simple deployment of intelligent nodes, however, wireless devices require power – historically this meant pulling a lot of wires or installing and replacing batteries. Devices powered by energy harvesters are maintenance-free and independent of batteries or other external energy sources, paving the way to a simpler installation of millions of devices connected to each other and the Internet.

Energy from the surroundings
Due to the energy harvesting principle the wireless modules gain their power from the surrounding environment and therefore work without batteries. In the process, an electrodynamic energy converter uses mechanical motion or a miniaturised solar module generating energy from light. Combining a thermoelectric converter with a DC/DC converter taps heat as an energy source. Even these small amounts of harvested energy are sufficient to transmit a wireless signal. The addition of a capacitor can ensure adequate power storage to bridge intervals when little or no energy can be harvested.

For optimal radio frequency (RF) effectiveness, the radio protocol, standardised as ISO/IEC 14543-3-10, uses sub 1 GHz frequency bands. This provides a safeguard against other wireless transmitters, whilst offering fast system response and elimination of data collisions. In addition, sub-GHZ radio waves have twice the range of 2.4 GHz signals for the same energy budget, and better penetration within buildings.

As a reference point, duplicating the energy harvesting wireless system at 2.4 GHz system requires about four times more receiver nodes to cover the same area. That increases its cost compared to a sub-GHz solution, for example. RF reliability is assured because wireless signals are just 0.7 milliseconds in duration and are transmitted multiple times for redundancy. The range of energy harvesting wireless sensors is about 300 meters in an open field and up to 30 meters inside buildings.

Building automation as a model for M2M
Energy harvesting devices are particularly attractive as replacements for batteries in low-power electronic systems such as wireless sensor networks, because of the logistics involved in the time-consuming tasks of acquiring, installing, and changing the batteries. Today, energy harvesting wireless technology is very well established providing M2M solutions in the building automation sector, bridging the control of light, HVAC and other fields of building technology to smart home, smart metering and energy management systems.

Wireless and batteryless technology significantly eases energy monitoring and control in buildings with only little intervention into the existing systems. The wireless devices are highly flexible to install so that individual components, wall switches, sensors and relay receivers can be easily networked to form an intelligent system without complex cabling. In addition, dispensing with batteries eliminates the burdensome need to maintain the devices’ energy supply in a regular time period, which can be up to each year.

An example for such a flexible automation system is HVAC control. Here, a thermostat, VAV (Variable Air Volume) or fan coil controller receives information related to occupancy, temperature, humidity, window position or CO2 from the respective batteryless sensors and controls the opening and closing of valve actuators for radiators, or dampers for VAV systems. At the same time, the controller sends status information to a central building automation system, and receives control messages from the BAS system. This enables the building to be monitored from a central location, that can be remote from the building itself, and to implement building wide settings, such as holiday shutdown, for example.